Fuel cells have been demonstrated to be viable for vehicle and stationary applications. However, several problems remain relating to the durability of electrode materials, especially in vehicle applications where proton exchange membrane (PEM) electrode materials are expected to operate under a wide variety of conditions, including relatively dry conditions that may adversely affect operation of the electrode as well as durability and lifetime.
Referring to FIG. 1, is shown a schematic diagram of a conventional fuel cell 10, such as in a vehicle, including an organic membrane 12 with an anode electrode 12A and a cathode electrode 12B. Hydrogen H2 may be converted to 4 protons and 4 electrons at the anode, where the 4 protons may pass through the proton exchange membrane 12 and the 4 electrons may pass through an electrical circuit 14 to the cathode 12B where the 4 protons and 4 electrons may react with oxygen O2 to produce water.
There are several types of electrode catalysts known in the art including catalyst particles (e.g., noble metals including Pt) which are typically supported on carbon substrates, or where a thin film of catalyst is coated as a shell onto a core of another material, including another particle or a whisker (e.g., an elongated rod-like shape). In a conventional electrode, catalyst is mixed with an ionic conduction material, such as perfluorosulfonic acid (PFSA) polymer, in order to conduct proton across the electrode. In an electrode which made from a core-shell catalyst where Pt surface of each particles are in contact with each other, an alternative proton conduction mechanism can be achieved where proton (or adsorbed species) can transport on the surface of Pt. In this case, an additional ionic conduction material (e.g. PFSA) is not required. However, the surface conduction mechanism on Pt is suspected to be highly dependent to the water activity compared to PFSA. (For further discussion of surface transport mechanisms on Pt surfaces see J. McBreen, Journal of Electrochemical Society, May 1985, pp. 1112-6) In consequence, this kind of electrode is likely to suffer in performance in a dry condition.
In this invention, the electrode hydrophilicity was modified by incorporation of hydrophilic particles into the electrode. The higher hydrophilicity results in a higher water activity in the electrode which thus improves the proton (or adsorbed species) conduction via the Pt surface transport mechanism. The hydrophilic particle was design so that it modifies the local water activity close to the Pt surface, and allows sufficient gas transport of the reactant gases to the Pt.